Method and system for evaluating single-section well test based on discrete fracture network technology

Abstract

The invention provides a method and a system for evaluating a single-section well test based on a discrete fracture network technology. The method comprises the following steps: classifying fractures according to morphological characteristics of a fracture network; constructing a corresponding single-section well test interpretation model and a single-section well test mathematical model based on crack classification by using a discrete crack network technology; respectively inputting the well testing key parameters of each crack classification into a single-section well testing mathematical model, and drawing a single-section double logarithmic well testing curve of each crack classification based on a solving result; and analyzing the single-section double logarithmic well testing curve to obtain an evaluation conclusion of single-section well testing. According to the method, a discrete fracture model (DFN) is adopted for coupling matrix-fracture seepage, and the actual fracturing effect of the deep shale gas well and the complex degree of the fracture network are considered, so that the seepage characteristics of the complex fracture network are accurately represented; the influence of key parameters such as reservoirs and cracks on well test interpretation results is determined by establishing a single-section well test mathematical model, and the accuracy and reliability of well test fracturing effect evaluation under different crack classifications are improved.

Description

Technical Field

[0001] This invention belongs to the field of deep shale gas reservoir development technology, and in particular relates to a method and system for evaluating single-stage well tests based on discrete fracture network technology. Background Technology

[0002] After fracturing, the fracture network morphology and distribution near the main fracture surface in deep shale gas reservoirs become extremely complex, often forming a complex and unevenly distributed fracture network. Furthermore, the fracture heterogeneity between different fracturing sections is extremely high, and the complex fracture morphology severely restricts parameter inversion and evaluation. Currently, there is no systematic fracturing evaluation method available domestically or internationally for evaluating the post-fracturing effects of single-section fractures.

[0003] Existing technologies for characterizing fractured reservoirs include dual porosity (DP) models, dual permeability (DK) models, and multiple continuous action domain (MINC) models. However, these methods all assume that fractures uniformly divide the matrix, failing to accurately characterize the seepage characteristics of complex fracture networks. To conduct reservoir parameter inversion and fracturing effect evaluation after single-stage fracturing, it is urgently necessary to establish single-stage well test models under different fracture systems to quantitatively evaluate well and reservoir parameter information. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for evaluating single-stage well tests based on discrete fracture network technology. The method includes...

[0005] Collect and analyze the morphological characteristics of crack networks, and classify cracks based on these characteristics;

[0006] Using discrete fracture network technology, a corresponding single-segment well test interpretation model is constructed based on fracture classification;

[0007] A mathematical model for a single-stage well test is established, the interpretation model of the single-stage well test is quantitatively described, and the numerical solution of the mathematical model of the single-stage well test is solved.

[0008] The key parameters of well testing for each fracture category are input into the single-segment well testing mathematical model, and the single-segment double logarithmic well testing curves for each fracture category are plotted based on the numerical solution.

[0009] The evaluation conclusions of the single-segment double-logarithmic well test curves are obtained by analyzing the single-segment well test curves.

[0010] Furthermore, the crack classification includes: single-wing cracks, double-wing cracks, branch cracks, and string cracks.

[0011] Furthermore, the single-stage well test interpretation model includes: a single-wing fracture-discrete fracture model, a two-wing fracture-discrete fracture model, a branch fracture-discrete fracture model, and a string fracture-discrete fracture model.

[0012] Furthermore, the assumptions of the single-stage well test interpretation model include:

[0013] The well-tested reservoir was a closed, mean reservoir.

[0014] In a finite-conductivity fracture network, the reservoir is vertically penetrated by finite-conductivity fractures, so there is no need to consider factors such as fracture mechanical deformation.

[0015] The reservoir matrix and fracture fluids exchange with each other; therefore, pressure drop losses and gravity effects within the wellbore are not considered.

[0016] Consider the fluid flow in a single horizontal well after fracturing and pump shutdown, i.e. how the fluid flows and diffuses into the fracturing formation without external pumping force.

[0017] The secondary fracture network is poorly developed, so the contribution of the external region to the yield of the modified area needs to be considered.

[0018] Furthermore, the establishment of the single-stage well test mathematical model includes:

[0019] For the single-stage well test mathematical model, an initial state is set, and inner and outer boundary conditions are assumed;

[0020] Fluid exchange between the matrix and fractures, and between fractures, is represented by source and sink terms.

[0021] By adding the source and sink terms into the seepage equation, we obtain the matrix seepage equation and the fracture seepage equation.

[0022] The matrix seepage equation and fracture seepage equation are processed to obtain the numerical solution of the single-stage well test mathematical model.

[0023] Furthermore, the initial state is assumed by the single-stage well test mathematical model to be the initial reservoir pressure as P. i , which is represented as,

[0024] P k =P i (k∈[0,N f ])

[0025] Where k represents the fluid medium; when k = 0, it represents the matrix; when k ≠ 0, it represents the cracks, and the total number of cracks is N. f ;

[0026] The inner boundary conditions include, in the case of the single-stage well test mathematical model considering the influence of the well reservoir and the skin, assuming that the inner boundary conditions are constant production conditions, which are expressed as follows:

[0027]

[0028] Among them, P w P is the bottom hole pressure (0.1 MPa); s is the formation pressure (0.1 MPa); r is the skin factor; r is the formation radius (cm). w h is the well radius (cm); h is the formation thickness (cm); B is the fluid volume coefficient (cm). 3 / cm 3 ;q is the source and sink cm 3 / s; C is the well storage coefficient (cm) 3 / (0.1MPa); t is time in seconds;

[0029] The outer boundary conditions include the assumption that the outer boundary of the single-stage well test mathematical model is a closed boundary, which is expressed as follows:

[0030]

[0031] Furthermore, the calculation formulas for the source and sink terms are derived based on Darcy's law;

[0032] The source and sink terms representing the fluid exchange between the matrix and the fracture are denoted as follows:

[0033]

[0034] Where m represents the mechanism element, f represents the crack element, and T mf This represents the conductivity between the matrix element and the fracture element.

[0035] The sources and sinks representing fluid exchange between fractures are denoted as follows:

[0036]

[0037] Among them, T ff Indicates the conductivity between fracture elements.

[0038] Substituting the source and sink terms representing the fluid exchange between the matrix and the fracture into the seepage equation, we obtain the matrix seepage equation, which is:

[0039]

[0040] Where, φ 0 ρ represents the porosity of the matrix; ρ represents the density of the fluid (g / cm³). 3 ;q 0 cm represents the source and sink of fluid in the matrix. 3 / s;V 0 The volume of the matrix unit is expressed in cm. 3 . The velocity of the fluid in the matrix is ​​expressed in cm / s. The transfer function q...0,k This represents the volumetric flow rate (cm³) of fluid flowing from the matrix to the j-th fracture. 3 / s;

[0041] Substituting the source and sink terms representing fluid exchange between fractures into the seepage equation, we obtain the fracture seepage equation, which is:

[0042]

[0043] Where, φ k q represents the porosity of the k-th crack; k cm represents the source and sink of fluid in the k-th crack. 3 / s;V k The volume of the k-th crack element is expressed in cm³. 3 . Let q represent the fluid seepage velocity in the k-th fracture (cm / s). Transfer function q k,0 This represents the volumetric flow rate (cm³) of fluid flowing from the k-th crack into the matrix. 3 / s. Transfer function q k,j This represents the volumetric flow rate (cm³) of fluid flowing from the k-th fracture to the j-th fracture. 3 / s.

[0044] Furthermore, the numerical solution of the single-stage well test mathematical model includes discretizing the matrix flow equation and fracture flow equation using the backward Euler method and the finite volume method, as expressed in the following formula:

[0045]

[0046] Where Δt is the time step s; R m and R fi , respectively, are the residual values ​​of the matrix and fracture seepage equations, in g / s. (n+1) represents the next state, and n represents the current state.

[0047] Furthermore, the key parameters for well testing include key reservoir parameters and key matrix parameters.

[0048] A system for evaluating single-stage well tests based on discrete fracture network technology includes: a fracture classification module, a single-stage well test interpretation model establishment module, a single-stage well test mathematical model establishment module, a single-stage double logarithmic well test curve plotting module, and a single-stage well test evaluation module;

[0049] The crack classification module classifies cracks according to the complexity of the crack network, accurately characterizing the morphological features of each crack after fracturing.

[0050] The single-stage well test interpretation model building module utilizes discrete fracture network technology and constructs a corresponding single-stage well test interpretation model based on fracture classification from the fracture classification module.

[0051] The single-stage well test mathematical model establishment module substitutes the fluid exchange between the matrix and fractures, and between fractures, into the seepage equation in the form of source and sink terms to obtain the analytical expressions of the matrix seepage equation and the fracture seepage equation, and solves the numerical solution of the single-stage well test mathematical model.

[0052] The single-segment double-logarithmic well test curve plotting module inputs key well test parameters and uses the single-segment well test interpretation model and mathematical model to plot the single-segment double-logarithmic well test curve.

[0053] The single-segment well test evaluation module evaluates the single-segment double logarithmic well test curve and obtains the evaluation conclusion of the single-segment well test.

[0054] Compared with the prior art, the present invention has the following advantages:

[0055] 1. This invention proposes a method and system for evaluating single-stage well testing based on discrete fracture network technology. It uses a discrete fracture model (DFN) to couple matrix-fracture seepage, taking into account the actual fracturing effect and the complexity of the fracture network in deep shale gas wells, thereby accurately characterizing the seepage characteristics of complex fracture networks.

[0056] 2. This invention establishes a single-stage well test mathematical model to determine the influence of key parameters such as reservoir and fracture on well test interpretation results, thereby improving the accuracy and reliability of fracturing effect evaluation under different fracture classifications.

[0057] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0059] Figure 1 The flowchart of a method for evaluating a single-stage well test based on discrete fracture network technology according to the present invention is shown.

[0060] Figure 2A schematic diagram of a single-stage well test evaluation system based on discrete fracture network technology according to the present invention is shown.

[0061] Figure 3 A schematic diagram of the single-wing slit mesh system in an embodiment of the present invention is shown.

[0062] Figure 4 A schematic diagram of the two-winged seam mesh system in an embodiment of the present invention is shown.

[0063] Figure 5 A schematic diagram of the branched seam mesh system in an embodiment of the present invention is shown.

[0064] Figure 6 A schematic diagram of the serial stitch mesh system shown in an embodiment of the present invention is illustrated.

[0065] Figure 7 A schematic diagram of the single-wing slot-discrete crack network model established in an embodiment of the present invention is shown.

[0066] Figure 8 A schematic diagram of the two-wing slot-discrete crack network model established in an embodiment of the present invention is shown.

[0067] Figure 9 A schematic diagram of the branch-discrete crack network model established in an embodiment of the present invention is shown.

[0068] Figure 10 A schematic diagram of the serial crack-discrete crack network model established in an embodiment of the present invention is shown.

[0069] Figure 11 The diagram shows a single-segment, double-logarithmic well test curve plotted in an embodiment of the present invention.

[0070] Figure 12 The diagram shows a single-segment double-logarithmic well test curve plotted in an embodiment of the present invention.

[0071] Figure 13 The diagram shows a single-segment double logarithmic well test curve of a branch fracture plotted in an embodiment of the present invention.

[0072] Figure 14 The diagram shows a single-segment double logarithmic well test curve of a series of fractures as plotted in an embodiment of the present invention.

[0073] Figure 15 The diagram shows the logarithmic well test curves for different fracture mesh systems plotted in embodiments of the present invention.

[0074] Figure 16 The single-section double logarithmic well test curve of well N1 in a certain block of deep shale gas reservoir in southern Sichuan is shown.

[0075] Figure 17This diagram illustrates the results of a permeability sensitivity analysis of the N1 well in a certain block of a deep shale gas reservoir in southern Sichuan.

[0076] Figure 18 This diagram illustrates the results of a permeability sensitivity analysis of the outer zone of well N1 in a certain block of a deep shale gas reservoir in southern Sichuan.

[0077] Figure 19 This diagram shows the results of the sensitivity analysis of the pressure conductivity coefficient in the inner zone of well N1 in a certain block of a deep shale gas reservoir in southern Sichuan.

[0078] Figure 20 This diagram illustrates the results of a sensitivity analysis of the external pressure conductivity coefficient of well N1 in a certain block of a deep shale gas reservoir in southern Sichuan.

[0079] Figure 21 This diagram illustrates the results of a sensitivity analysis of fracture conductivity in well N1 of a deep shale gas reservoir in southern Sichuan.

[0080] Figure 22 This diagram illustrates the results of a sensitivity analysis of the well-reservoir coefficient of well N1 in a certain block of deep shale gas reservoirs in southern Sichuan.

[0081] Figure 23 This diagram illustrates the skin coefficient sensitivity analysis results of well N1 in a certain block of a deep shale gas reservoir in southern Sichuan. Detailed Implementation

[0082] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0083] like Figure 1 As shown, a method for evaluating a single-stage well test based on discrete fracture network technology includes the following steps:

[0084] S1. Collect and analyze the morphological characteristics of the crack network, and classify the cracks according to the morphological characteristics of the crack network.

[0085] After a reservoir undergoes large-scale hydraulic fracturing, multiple secondary fractures will form around the main hydraulic fracture. These secondary fractures will continue to expand to form multi-level fractures, thus creating a complex fracture network.

[0086] This invention classifies cracks based on the morphological characteristics of the crack network, thereby accurately characterizing the morphology of each segment of the crack after hydraulic fracturing.

[0087] Alternatively, such as Figures 3-6As shown, the present invention classifies cracks into four categories, including single-wing cracks, two-wing cracks, branch cracks, and string cracks.

[0088] S2. Establishment of Discrete Crack Network (DFN) model;

[0089] Discrete crack network (DFN) technology can explicitly characterize crack properties, including different orientations, sizes, spatial distributions, morphological features, and transmission rates.

[0090] Using Discrete Fracture Network (DFN) technology, a corresponding single-segment well test interpretation model is constructed based on fracture morphology classification.

[0091] Alternatively, such as Figures 7-10 As shown, this invention establishes corresponding single-section well test interpretation models based on four different fracture classifications, including: single-wing fracture-discrete fracture model, two-wing fracture-discrete fracture model, branch fracture-discrete fracture model, and string fracture-discrete fracture model.

[0092] Optionally, the assumptions set in the single-stage well test interpretation model include:

[0093] a. Seal off the mean reservoir to make it bounded and horizontal with uniform thickness;

[0094] b. Limited-conductivity fracture network: The reservoir is vertically penetrated by limited-conductivity fractures, so there is no need to consider factors such as fracture mechanical deformation.

[0095] c. The reservoir matrix and fracture fluids exchange with each other; therefore, pressure drop loss and gravity effects within the wellbore are not considered.

[0096] d. The main consideration is the fluid flow in a single horizontal well after fracturing and pumping is stopped, i.e., how the fluid flows and diffuses into the fracturing formation without external pumping force.

[0097] e. The secondary fracture network is poorly developed, so the contribution of the external region to the yield of the modified region needs to be considered.

[0098] S3. Establishment of Mathematical Model for Single-Stage Well Testing

[0099] A mathematical model for single-stage well testing is established to quantitatively describe the established interpretation model and solve the numerical solution to obtain the pressure response of the reservoir.

[0100] S3.1 is a mathematical model for a single-stage well test, setting the initial state and assuming inner and outer boundary conditions.

[0101] S3.1.1 The single-stage well test mathematical model assumes the initial reservoir pressure is Pi, which is expressed as follows:

[0102] P k =Pi (k∈[0,N f ])

[0103] Where k is the fluid medium, when k = 0, it represents the matrix, when k ≠ 0, it represents the crack, and the total number of cracks is Nf;

[0104] S3.1.2 The single-stage well test mathematical model considers the influence of the well reservoir and the skin, and assumes that the inner boundary conditions are constant production conditions. Its formula is:

[0105]

[0106] S3.1.3 The mathematical model for the single-stage well test assumes that the outer boundary is a closed boundary, and its formula is as follows:

[0107]

[0108] In the above formula, P w P is the bottom hole pressure (0.1 MPa); s is the formation pressure (0.1 MPa); r is the skin factor; r is the formation radius (cm). w h is the well radius (cm); h is the formation thickness (cm); B is the fluid volume coefficient (cm). 3 / cm 3 ;q is the source and sink cm 3 / s; C is the well storage coefficient. t represents time s.

[0109] S3.2 To couple the seepage between matrix, matrix-crack, and crack-crack, the fluid exchange between matrix-crack and crack-crack is represented by source and sink terms, and its calculation formula is derived based on Darcy's law.

[0110] S3.2.1, the source and sink terms representing the fluid exchange between the matrix and the fracture are expressed as follows:

[0111]

[0112] Among them, T mf This represents the conductivity between the matrix element and the fracture element.

[0113] S3.2.2, the source and sink terms representing fluid exchange between fractures are expressed as follows:

[0114]

[0115] Among them, T ff This represents the conductivity between fracture elements.

[0116] S3.3. The source and sink terms representing fluid exchange between the matrix and fractures, and between fractures themselves, are added to their respective seepage equations to obtain analytical expressions for the matrix seepage equation and the fracture seepage equation. S3.3.1. The matrix seepage equation is as follows:

[0117]

[0118] Where, φ 0 ρ represents the porosity of the matrix; ρ represents the density of the fluid, in g / cm³. 3 ;q 0 Indicates the source and sink of fluids in the matrix, cm 3 / s;V 0 The volume of the matrix unit is expressed in cm. 3 . The velocity of the fluid in the matrix is ​​expressed in cm / s. The transfer function q... 0,j This represents the volumetric flow rate of fluid from the matrix to the j-th fracture, expressed in cm³. 3 / s

[0119] S3.3.2, The fracture seepage equation is as follows:

[0120]

[0121] Where, φ k q represents the porosity of the k-th crack; k cm represents the source and sink of fluid in the k-th crack. 3 / s;V k The volume of the k-th crack element is expressed in cm³. 3 . Let q represent the fluid seepage velocity in the k-th fracture (cm / s). Transfer function q k,0 This represents the volumetric flow rate (cm³) of fluid flowing from the k-th crack into the matrix. 3 / s. Transfer function q k,j This represents the volumetric flow rate (cm³) of fluid flowing from the k-th fracture to the j-th fracture. 3 / s.

[0122] S3.4. The seepage equation in step S3.2 is discretized using the backward Euler method and the finite volume method, and then the numerical solution of the single-stage well test mathematical model is solved to obtain the reservoir pressure response, which is expressed by the formula:

[0123]

[0124] Where Δt is the time step s; R m and , where g / s are the residual values ​​of the matrix and fracture seepage equations, respectively. (n+1) represents the next state, and n represents the current state.

[0125] S4, such as Figures 11-14 As shown, the key parameters of well testing under different fracture classifications are input into the established single-segment well testing mathematical model to plot the single-segment double logarithmic well testing curve.

[0126] Optionally, the key parameters for well testing include key reservoir parameters and key fracture parameters;

[0127] Based on the application background of single-stage fracturing pump shutdown pressure drop, only the single-stage fracturing part of horizontal wells is considered.

[0128] S5. Analyze the single-section well test curves under different fracture classifications to obtain the evaluation results of different types of single-section well tests.

[0129] Alternatively, as shown in the appendix Figure 15 As shown, by analyzing the single-segment double-logarithmic well test curves under different fracture classifications plotted above, the following evaluation results are obtained.

[0130] (1) The single-winged slit has poor connectivity with the reservoir matrix, and both the pressure curve and the pressure derivative curve are low.

[0131] (2) No matrix-crack crossflow characteristics were observed in single-wing and double-wing cracks; in branch cracks, string cracks, and complex crack networks, the complexity of cracks increased, and the pressure reciprocal curve gradually shifted to the left and became more obvious.

[0132] In another embodiment of the present invention, based on the single-stage fracturing and pump shutdown data of well N1 in a certain block of deep shale reservoir in southern Sichuan, the serial fracture-discrete fracture model established in this invention is used to carry out case application analysis.

[0133] Input the key parameters of the reservoir and fractures in well N1, as shown in Tables 1 and 2.

[0134] Table 1

[0135]

[0136] Table 2

[0137]

[0138] like Figure 15 As shown, the established single-section well test model of well N1 is calculated, and the double logarithmic well test curve is plotted.

[0139] According to the interpretation results of the single-section well test of well N1, the permeability of the fracture network area of ​​well N1 is 1 mD, the effective seepage half length of the fracture is 60 m, and the fracture conductivity is 40 mD·m.

[0140] Meanwhile, based on the well testing software Saphir, sensitivity analyses were conducted on parameters such as inner zone permeability (0.5–2 mD), outer zone permeability (0.1–1 mD), inner zone pressure conductivity (14.78–295.57 m² / h), outer zone pressure conductivity (7.39–29.56 m² / h), fracture conductivity (30–120 mD·m), well-reservoir coefficient (0.005–0.1 m³ / MPa), and skin coefficient (1 × 10⁻⁵–1).

[0141] like Figures 16-22 As shown, the analysis results are as follows:

[0142] (1) The well reservoir coefficient and the skin coefficient mainly affect the time when the curve hump appears and the height of the hump;

[0143] (2) The crack conductivity mainly affects the curve and causes a decrease to varying degrees in the middle and later stages;

[0144] (3) The permeability and pressure conductivity of the inner zone mainly affect the mid-term curve;

[0145] (4) The permeability and pressure coefficient of the outer zone mainly affect the middle and later stages of the curve. The smaller the permeability of the outer zone, the more obvious the "concave" curve is.

[0146] like Figure 2 As shown, a system for evaluating single-stage well testing based on discrete fracture network technology includes a fracture classification module, a single-stage well testing interpretation model establishment module, a single-stage well testing mathematical model establishment module, a single-stage double logarithmic well testing curve plotting module, and a single-stage well testing evaluation module.

[0147] The crack classification module classifies cracks according to the complexity of the crack network, accurately characterizing the morphological features of each crack after fracturing.

[0148] The single-stage well test interpretation model building module utilizes discrete fracture network technology and constructs a corresponding single-stage well test interpretation model based on fracture classification from the fracture classification module.

[0149] The single-stage well test mathematical model establishment module substitutes the fluid exchange between the matrix and fractures, and between fractures, into the seepage equation in the form of source and sink terms to obtain the analytical expressions of the matrix seepage equation and the fracture seepage equation, and solves the numerical solution of the single-stage well test mathematical model.

[0150] The single-segment double-logarithmic well test curve plotting module inputs key well test parameters and uses the single-segment well test interpretation model and mathematical model to plot the single-segment double-logarithmic well test curve.

[0151] The single-segment well test evaluation module performs the single-segment double-logarithmic well test curve and obtains corresponding conclusions.

[0152] The foregoing description and accompanying drawings fully illustrate embodiments of the invention to enable those skilled in the art to practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Some portions and features of some embodiments may be included or substituted for portions and features of other embodiments. Embodiments of the invention are not limited to the structures described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from their scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for evaluating a single-stage well test based on discrete fracture network technology, characterized in that, The method includes, Collect and analyze the morphological characteristics of crack networks, and classify cracks based on these characteristics; Using discrete fracture network technology, a corresponding single-segment well test interpretation model is constructed based on fracture classification; A mathematical model for a single-stage well test is established, the interpretation model of the single-stage well test is quantitatively described, and the numerical solution of the mathematical model of the single-stage well test is solved. The key parameters of well testing for each fracture category are input into the single-segment well testing mathematical model, and the single-segment double logarithmic well testing curves for each fracture category are plotted based on the numerical solution. The evaluation conclusions of the single-segment double-logarithmic well test curves are obtained by analyzing the single-segment well test curves.

2. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 1, characterized in that, The crack classification includes: single-wing crack, double-wing crack, branch crack, and string crack.

3. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 1, characterized in that, The single-stage well test interpretation model includes: single-wing fracture-discrete fracture model, two-wing fracture-discrete fracture model, branch fracture-discrete fracture model, and string fracture-discrete fracture model.

4. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 3, characterized in that, The assumptions of the single-stage well test interpretation model include: The well-tested reservoir was a closed, mean reservoir. In a finite-conductivity fracture network, the reservoir is vertically penetrated by finite-conductivity fractures, so there is no need to consider factors such as fracture mechanical deformation. The reservoir matrix and fracture fluids exchange with each other; therefore, pressure drop losses and gravity effects within the wellbore are not considered. Consider the fluid flow in a single horizontal well after fracturing and pumping is stopped, i.e. how the fluid flows and diffuses into the fracturing formation without external pumping force. The secondary fracture network is poorly developed, so the contribution of the external region to the yield of the modified area needs to be considered.

5. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 1, characterized in that, The establishment of a single-stage well test mathematical model includes: For the single-stage well test mathematical model, an initial state is set, and inner and outer boundary conditions are assumed; Fluid exchange between the matrix and fractures, and between fractures, is represented by source and sink terms. By adding the source and sink terms into the seepage equation, we obtain the matrix seepage equation and the fracture seepage equation. The matrix seepage equation and fracture seepage equation are processed to obtain the numerical solution of the single-stage well test mathematical model.

6. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 5, characterized in that, The initial state is assumed in the single-stage well test mathematical model to be the initial reservoir pressure as P. i , which is represented as, P k =P i (k∈[0,N f ]) Where k represents the fluid medium; when k = 0, it represents the matrix; when k ≠ 0, it represents the cracks, and the total number of cracks is N. f ; The inner boundary conditions include, in the case of the single-stage well test mathematical model considering the influence of the well reservoir and the skin, assuming that the inner boundary conditions are constant production conditions, which are expressed as follows: Among them, P w ρ is the bottom hole pressure; P is the formation pressure; s is the skin factor; r is the formation radius; r w λ is the well radius; h is the formation thickness; B is the fluid volume coefficient; q is the source and sink terms; C is the well-reservoir coefficient; t is time. The outer boundary conditions include the assumption that the outer boundary of the single-stage well test mathematical model is a closed boundary, which is expressed as follows:

7. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 5, characterized in that, The calculation formulas for the source and sink terms are derived based on Darcy's law; The source and sink terms representing the fluid exchange between the matrix and the fracture are denoted as follows: Where m represents the mechanism element, f represents the crack element, and T mf This represents the conductivity between the matrix element and the fracture element; The sources and sinks representing fluid exchange between fractures are denoted as follows: Among them, T ff This represents the conductivity between fracture elements; Substituting the source and sink terms representing the fluid exchange between the matrix and the fracture into the seepage equation, we obtain the matrix seepage equation, which is: Where, φ 0 ρ represents the porosity of the matrix; ρ represents the density of the fluid; q represents the density of the fluid. 0 V represents the source and sink of fluids in the matrix. 0 This indicates the volume of the matrix unit. This represents the seepage velocity of the fluid in the matrix. Transfer function q 0,j This represents the volumetric flow rate of fluid flowing from the matrix to the j-th fracture; Substituting the source and sink terms representing fluid exchange between fractures into the seepage equation, we obtain the fracture seepage equation, which is: Where, φ k q represents the porosity of the k-th crack; k V represents the source and sink of fluid in the k-th crack; k This represents the volume of the k-th crack element. Let q represent the seepage velocity of the fluid in the k-th fracture. Transfer function q k,0 This represents the volumetric flow rate of fluid flowing from the k-th fracture into the matrix. Transfer function q k,j This represents the volumetric flow rate of fluid flowing from the k-th crack to the j-th crack.

8. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 5, characterized in that, The numerical solution to the mathematical model of the single-stage well test includes discretizing the matrix flow equation and fracture flow equation using the backward Euler method and the finite volume method, as expressed in the following formula: Where Δt is the time step; R m and , respectively, are the residual values ​​of the matrix and fracture seepage equations, in g / s. (n+1) represents the next state, and n represents the current state.

9. The method for evaluating a single-stage well test based on discrete fracture network technology according to claim 1, characterized in that, The key parameters for well testing include reservoir key parameters and matrix key parameters.

10. A system for evaluating single-stage well tests based on discrete fracture network technology, comprising: The module includes a fracture classification module, a single-stage well test interpretation model establishment module, a single-stage well test mathematical model establishment module, a single-stage double-logarithmic well test curve plotting module, and a single-stage well test evaluation module. The crack classification module classifies cracks according to the complexity of the crack network, accurately characterizing the morphological features of each crack after fracturing. The single-stage well test interpretation model building module utilizes discrete fracture network technology and constructs a corresponding single-stage well test interpretation model based on fracture classification from the fracture classification module. The single-stage well test mathematical model establishment module substitutes the fluid exchange between the matrix and fractures, and between fractures, into the seepage equation in the form of source and sink terms to obtain the analytical expressions of the matrix seepage equation and the fracture seepage equation, and solves the numerical solution of the single-stage well test mathematical model. The single-segment double-logarithmic well test curve plotting module inputs key well test parameters and uses the single-segment well test interpretation model and mathematical model to plot the single-segment double-logarithmic well test curve. The single-segment well test evaluation module evaluates the single-segment double logarithmic well test curve and obtains the evaluation conclusion of the single-segment well test.

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